In exploring links between climate change and human illness, significant attention has been given to the potential impact of such change on harmful algal bloom (HAB) populations and the illnesses that they cause. Among the various HAB-related human diseases, ciguatera has the greatest public health and economic impact, with recent studies from French Polynesia linking ciguatera incidence with increasing seawater temperatures: as such, ciguatera may serve as a key "sentinel" disease for global warming. We are proposing to build on the approach used in the South Pacific climate/ciguatera studies, but with a shift in focus to the Caribbean and "Caribbean ciguatera," taking advantage of our long-standing base for epidemiologic and environmental studies in the U.S. Virgin Islands. We hypothesize that climatic disturbances/disruptions of reef areas result in overgrowth of species of the dinoflagellate Gambierdiscus, with subsequent, and predictable, increases in fish toxicity and ciguatera incidence in endemic areas. To explore this hypothesis, we are proposing 1) to identify and characterize hospital and clinic-based ciguatera cases on St. Thomas and St. John;and to conduct cross-sectional surveys to develop accurate community-based estimates of disease incidence. As a second component of the study, we will monitor Gambierdiscus populations at sentinel sites around St. Thomas, looking at dinoflagellate distribution, abundance, and population structure;and collect data on toxin concentrations and structural diversity in dinoflagellates, locally caught fish, and fish/fish remnants implicated as the cause of ciguatera cases. Finally, we will seek to correlate weather patterns, including, in particular, the Atlantic Warm Pool, with prospective dinoflagellate population data, and prospective and retrospective disease incidence data;and to develop predictive models for occurrence of illness in human populations. The project explores the hypothesis that climatic disturbances/disruptions of reef areas result in overgrowth of species of the dinoflagellate Gambierdiscus, with subsequent, and predictable, increases in fish toxicity and incidence of ciguatera fish poisoning in endemic areas. The study will be performed on the islands of St. Thomas and St. John, U.S. Virgin Islands;data will be collected on ciguatera incidence, and on dinoflagellate populations implicated as the source of the toxins that cause the disease.